1. Field of the Invention
This invention relates to a coiled slide fastener element produced by bending a monofilament of synthetic resin, and more particularly to the structure of a coupling head portion for such a coiled slide fastener element.
2. Description of the Related Art
There are currently known a variety of coupling head portions for such slide fasteners which are produced by stamping a monofilament or pressing the monofilament by using force to wind the monofilament around a substantially square mandrel, for example. In these methods, the coupling head portion is formed by bending and pressing the monofilament by applying force.
One example of such a coupling head portion is shown in FIGS. 7 and 8 of the accompanying drawings. A coupling head portion 12 is small in thickness, and bulging portions 13 have steep slopes 14.
With this coupling head portion, the slopes of the bulging portions are recessed as shown by a solid line in FIG. 8. Preferably these slopes should be gentle or curved as shown by a double-dot line in FIG. 8. Conventionally, these slopes are rather deeply recessed, thereby making the coupling head portion small in size and in thickness. When a pair of mating coupling elements of a slide fastener are coupled, such coupling head portions have somewhat weak lateral coupling force, and tend to be disengaged if pulled strongly in the lateral direction.